The present invention relates to a method for alarming decrease in tire air-pressure and an apparatus therefor. More particularly, it relates to a method for alarming decrease in tire air-pressure and an apparatus therefor for detecting decrease in air pressure of tires used, for instance, for trucks or buses in which differences in tread widths (axle distances between right and left tire positions) between front and rear wheels are large.
Apparatuses for detecting decrease in tire air-pressure through relative comparison of wheel speeds have been conventionally proposed (e.g. Japanese Examined Patent Publication No. 55322/1993). According to this publication, there are employed various methods for improving the accuracy of detection such as performing comparison of respective sums of wheel speeds of diagonally positioned wheels or performing judgement only in the case where the vehicle is in a straight-ahead running condition in which disturbance factors are limited. However, judgement needs to be preformed even in the case where the vehicle is making a turn since the chance of detecting decompression is decreased. Further, there have been proposed methods of correcting disturbances (influences) during turning as a function in which lateral acceleration is incorporated in the determined value. Examples of such methods are disclosed, for instance, in Japanese Unexamined Patent Publication No. 8713/1994, Japanese Unexamined Patent Publication No. 501040/1996 or Japanese Unexamined Patent Publication No. 164720/1996.
The above-mentioned correction based on lateral acceleration does not present problems in case of passenger cars in which differences in tread widths between front and rear wheels are small. However, in case of vehicles in which differences of tread widths between front and rear wheels are large such as trucks or buses which mostly have multiple wheels as their rear wheels, determination errors cannot be sufficiently corrected so that it is presented a drawback that it is difficult to improve the determination accuracy.
In view of these facts, it is an object of the present invention to provide a method for alarming decrease in tire air-pressure and an apparatus therefor with which the accuracy of determining air-pressure can be improved.